(Dr. Celine Gounder is an internist, infectious diseases and public health specialist and medical journalist. The opinions expressed here are those of the author.)

By Celine Gounder

Aug 14 (Reuters) - The Ebola outbreak continues to spread in Guinea, Liberia and Sierra Leone, the countries hardest hit by the disease. More than 1,000 people have now died from the virus. The Centers for Disease Control and Prevention has issued its highest-level alert for a response to the Ebola crisis. The World Health Organization has declared the outbreak a Public Health Emergency of International Concern. The disease is intensifying in West Africa, but the epidemic poses minimal risk to Americans. So why are we so afraid?

Scientists think about the risk of Ebola in terms of how likely someone will get it and die. That probability of someone in this country dying from Ebola is miniscule. But how the average person thinks about risk is more complicated. Other factors - including fear of the exotic, dramatic and gruesome - heighten our anxieties and capture our imaginations.

The Zaire strain of Ebola out of control in West Africa is the most virulent form of the virus and comes from the "heart of darkness" itself. Many Americans still think of Africa as a failed continent plagued by disease, poverty and war - and we're afraid of it. There's a certain xenophobia to our fear of Ebola. Representatives Phil Gingrey (R-Ga.), Todd Rokita (R-Ind.) and Larry Buschon (R-Ind.) have gone so far as to voice concerns that the children from Central America crossing the U.S.-Mexico border might be carrying the Ebola virus. Gingrey is an obstetrician and Buschon a heart surgeon. But there is no Ebola in Central America.

We picture the disease liquefying organs and its victims spewing blood and other bodily fluids, eventually bleeding to death. But Ebola kills by lowering blood pressure and weakening the immune system. When vital organs don't receive enough blood, they fail and die. When the immune system is impaired, the risk of other infections increases. Ebola can cause problems with blood clotting, but this typically causes oozing not massive bleeding.

We're far more likely to die of heart disease, stroke or diabetes in this country, but these diseases are familiar and don't terrify us like Ebola. It is, to some extent, normal to downplay the risks that we have to live with everyday. We continue to smoke, eat poorly and not exercise even though these behaviors put us at real risk. More than 50,000 Americans die of influenza and pneumonia each year, but we still don't get our shots.

We've learned about Ebola from the news media and our social networks, but this information is skewed. The media cover accidents, threats and rare or dramatic events. I have been asked if HIV is still a problem because it's not in the news anymore. About 1.5 million people annually die of HIV worldwide, and almost as many die from tuberculosis. But this isn't new, so it rarely makes headlines. "Scary" health stories make for better news. The media are bombarding us with dramatic, minute-to-minute coverage of the Ebola epidemic, which fuels our anxieties. And once we're scared, it is hard to "unscare" us. Meanwhile, our social networks, the power of which has been amplified by the rise of social media, tend to validate and magnify our fears.

The CDC, the government agency leading the U.S. response to the Ebola crisis, is doing what it can to help us understand the disease and what is being done to control it. But the agency has a public relations problem. For one thing, its work is highly technical and poorly understood by the public. You also don't hear about everything the CDC does right to protect the nation's health. You only hear about what goes wrong.

Earlier this year, the CDC inappropriately shipped the deadly H5N1 strain of influenza to a Department of Agriculture lab. (No one was exposed.) In June, agency employees were exposed to anthrax due to mishandling of laboratory specimens. And in July, we learned that vials of live smallpox virus had been discovered in a Food and Drug Administration laboratory, previously operated by the National Institutes of Health. These events eroded public trust in the nation's health agencies at a time when we most need to trust them. (Celine Gounder)